Prevention of unauthorized movement of articles between predetermined areas

ABSTRACT

A system for indicating an attempt to move an article, such as a piece of baggage or an article of merchandise, between predetermined areas, by providing a radio transmitter and radio receiver between the areas, and providing on the article a device having electrical circuitry adapted to receive from the transmitter a signal at a first frequency, and retransmit a radio signal of changed frequency, with the receiver being constructed to respond to and indicate the presence of the return signal. A person authorized to move the baggage or other article may have a key adapted to disable the circuitry against transmission of the changed frequency signal, or otherwise alter the signal, in a manner indicating to the receiver his authorization.

United States Patent [72] inventor Wendell S. Miller 1341 Comstock Ave.,Los Angeles, Calif. 90024 [21] Appl. No. 809,259 [22] Filed Mar. 21,1969 [45] Patented Sept. 28, 1971 [54] PREVENTION OF UNAUTHORIZEDMOVEMENT 0F ARTICLES BETWEEN PREDETERMINED AREAS 16 Claims, 6 DrawingFigs.

[52] US. Cl 340/280, 325/8, 325/29, 340/152 TR, 340/171, 340/224,340/276 [51] Int. Cl. ...G08b 13/14 [50] Field of Search 340/152 TR,312, 258, 280, 276, 224, 420, 421,171; 325/8,16, 21, 29

[56] References Cited UNITED STATES PATENTS 3,098,971 7/1963 Richardson340/258 3,175,047 3/1965 Borberg 340/280 3,299,424 1/1967 Vinding340/258 3,478,344 11/1969 Schwitzgebel et al. 340/280 3,493,955 2/1970Minasy 340/280 Primary Examiner-John W. Caldwell Assistant Examiner-J.Michael Bobbitt Attorney-William P. Green ABSTRACT: A system forindicating an attempt to move an article, such as a piece of baggage oran article of merchandise, between predetermined areas, by providing aradio transmitter and radio receiver between the areas, and providing onthe article a device having electrical circuitry adapted to receive fromthe transmitter a signal at a first frequency, and retransmit a radiosignal of changed frequency, with the receiver being constructed torespond to and indicate the presence of the return signaL A personauthorized to move the baggage or other article may have a key adaptedto disable the circuitry against transmission of the changed frequencysignal, or otherwise alter the signal, in a manner indicating to thereceiver his authorization.

1 PREVENTION OF UNAUTHORIZED MOVEMENT OF ARTICLES BETWEEN PREDETERMINEDAREAS BACKGROUND OF THE INVENTION This invention relates generally toapparatus and methods for indicating whether a particular person isauthorized to move a certain piece of baggage or other article betweentwo different areas.

In the baggage room of an airport or the like, great difficulty isencountered in attempting to maintain any effective control againstunauthorized removal or theft of a suitcase from the area. Large numbersof bags frequently arrive at the pickup zone simultaneously, and must bedistributed to many different travelers in a very short period of timewith minimum inconvenience to the travelers. Attempts to compare checknumbers at an exit location have resulted is such excessive slowing ofthe overall rate of movement of baggage and persons through the areathat in many airports all such attempts at checking have been abandoned.

Similarly, in a store or other establishment having merchandise or otherarticles on display at accessible locations, it is very difficult todetect an attempt at removal of an article from the store or from aparticular area of the store. The article may be completely concealed bythe taker within a handbag, box, piece of clothing, or the like, in amanner rendering it almost impossible to detect the article as it iscarried from the store.

SUMMARY OF THE INVENTION The present invention provides apparatus andmethods for indicating very rapidly and conveniently whether a personwho is attempting to move a particular article, such as a suitcase, itemof merchandise, identification badge, or the like, between two areas, isauthorized for such movement. The indication of authorization ornonauthorization may be given in any desirable manner, as by an audibleor visual signal, by opening or closing a door or gate at an exit orentrance loca tion, or in any of numerous other ways.

The desired monitoring result is attained by providing radio equipmentat or near the controlled area which coacts with a very simple device onthe bag or other article in a manner giv ing the indication ofauthorization or nonauthorization. The circuit on the article may be aminiaturized extremely low cost integrated circuit, which may beenergized completely by power received from the primary radio equipmentnear the exit location, without the necessity for provision of asupplementary power source on the individual articles being controlled.

In applying the present invention to the control of baggage and certainother types of articles, I preferably provide in conjunction with thecircuitry on the bag a control unit or control means which is actuableonly by an authorized person, and which upon actuation will indicate tothe fixed radio equipment that the person is authorized. For example,this control unit may take the form of a key which is carried by theauthorized person, and is capable of converting the circuitry on the bagor other article to a condition indicating authorization of the personusing the key. Alternatively, a combination lock or other control unitmay be substituted for the key.

For maximum simplicity, the circuitry carried by the article beingcontrolled desirably constitutes a transponder circuit which is adaptedto receive a radio signal of predetermined frequency from a fixedtransmitter at the exit location, and which then transmits a responsesignal at a changed frequency to which the fixed receiver is tuned. lnmost instances, the frequency emitted by the transponder circuitry maybe a multiple or harmonic of the original received frequency, in whichevent a simple rectifier circuit may function to change the frequency.It is also contemplated, however, that other frequencies may be emittedby the transponder, such as a subharmonic frequency or a nonharmonicfrequency produced by a heterodyne circuit in the transponder in whichtwo frequencies received from the main transmitter are mixed to producesum and difference frequencies.

BRIEF DESCRIPTION OF THE DRAWING The above and other features andobjects of the invention will be better understood from the followingdetailed description of the typical embodiments illustrated in theaccompanying drawing, in which:

FIG. I is a diagrammatic representation of an airport baggage area, orother area to which the invention is to be applied;

- FIG. 2 illustrates fragmentarily-in perspective a suitcase which maybe located within the baggage area of FIG. l, and which carries aresponse circuit for indicating when an attempt is made to remove thebag by an unauthorized person;

FIG. 3 is a greatly enlarged fragmentary section taken on line 3-3 ofFIG. 2, and showing a key positioned within the bag carried device ofFIG. 2;

FIG. 4 illustrates diagrammatically the circuitry of the bag carrieddevice;

FIG. 5 shows the preferred wave form of the two radio signals utilizedin the apparatus; and

FIG. 6 shows a variational form of the invention which is adapted forattachment to an article of merchandise, and which may not be keyactuated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the FIG. 1 diagram, a roomor area to be policed by equipment embodying the present invention isillustrated generally at 10, being bounded by walls I], and typicallyhaving entrance 12 through which persons may enter the room, and an exitopening or doorway 13 through which persons leave the room. As exemplaryof one preferred use of the invention, the room or area 10 may beconsidered as constituting a baggage reception area in an airport or thelike, having a conveyor represented at 14 along which the individualbags 15 are advanced into the room and onto a support surface orplatform 16 from which the individual tourists may select their variousbags. After a person has obtained all of his baggage from the platform16, he leaves the room through exit 13, and in doing so must passcertain stationary equipment 17 positioned adjacent the exit doorway fordetermining whether the person attempting to remove a particular pieceof baggage is authorized to do so. For coaction with the stationaryequipment 17, individual pieces of baggage are provided with atransponder unit 18 (FIGS. 2 and 3) which is preferably controlled by akey 19 kept in the possession of the person owning the bag.

The fixed equipment 17 adjacent or near exit 13 includes a radiotransmitter 20 which emits a preferably continuous and unchanging radiowave of a predetermined frequency, desirably a frequency within one of.the industrial bands. In FIG. 5 the sinusoidal voltage curve of thatwave emitted by transmitter 20 is represented at 21. Also near oradjacent exit opening 13 there is provided a stationary radio receiver22 (FIG. 1), which is tuned to receive and respond to a radio wave of apredetennined frequency different than that emitted by transmitter 20.Preferably, receiver 22 is responsive only or primarily to a radio wavewhose frequency is a predetermined multiple or harmonic of (desirablythe second harmonic of) the radio wave emitted by transmitter 20. Anindicating unit 23 is controlled by receiver 22 and is energized toproduce an appropriate indication when a signal of the predeterminedharmonic frequency is received by receiver 22. The indicator unit 23 maytypically be a horn, bell, or other audible signal, a light, sign orother visual signal, or any other type of indicator whose energizationindicates to an attendant that a particular person carrying a bag pasttransmitter 20 and receiver 22 is not authorized to do so. Alternativelyor supplementally, the indication of authorization or nonauthorizationmay be given by automatic actuation of a turnstile 24 or other gatestructure at the exit location between passing and nonpassingconditions, under the control of receiver 22 in accordance with itsreception or nonreception of the predetermined harmonic frequency. It iscontemplated that the indications given by the system may function inany of numerous manners, to indicate by energization of the audible orother signal either that the person is authorized or not authorized, asdesired, and either to actuate a turnstile or gate from a normally openor passing condition to a closed or nonpassing position when anunauthorized person attempts to leave the area, or alternatively toactuate a normally closed or nonpassing turnstile or gate to an open orpassing condition when an authorized person desires to leave.

The transponder units or devices 18 carried by the individual bags aredesigned to receive the radio signals emitted by transmitter 20, and torespond thereby to transmission of a changed radio signal of theparticular type to which receiver 23 is tuned. As previously indicated,this signal to which the receiver is tuned is preferably a harmonic ofthe signal received by device 18 from fixed transmitter 20, for bestresults the second harmonic. To produce the second harmonic, the device18 may rectify the signal from transmitter 20, as represented by thesinusoidal wave 21 of FIG. 5, to the pulsating direct current conditionillustrated at 25 in FIG. 5, in which the frequency of pulsating wave 25is twice that of wave 21. The full wave rectified current is then passedthrough a transmitting antenna to transmit a radio wave from the device18 to receiver 22 at the second harmonic frequency.

FIG. 4 shows schematically at 26 a typical electrical circuit for thedevice 18. This circuit includes a receiving antenna coil represented at27, which feeds into a bridge-type full wave rectifier circuit 28, whoserectified output in the form of pulsating direct current as representedat 25 in FIG. 5 is passed through a transmitting antenna coil 29. Therectifier circuit includes four individual rectifier elements 30,typically of the solid-state variety.

Structurally, the entire circuit 26 illustrated in FIG. 4 may be formedas a very inexpensive highly miniaturized integrated circuit, formed ona single typically rectangular very thin and small chip 31 of silicon orthe like, on which the various components are formed by appropriatepainting or deposition techniques (see FIG. 3). More particularly, theantenna coils 27 and 29 may be painted on the silicon body 31 as thinlines of aluminum paint or other conductive material extending about thesilicon ship and along its outer surface. The diodes or rectifiers 30may be formed by appropriately doping localized portions of the surfaceof the silicon with N" and P material, as at the locations designated 30in FIG. 3. The electrical connections between the various parts, likethe coils, are formed by aluminum or other conductive lines painted onthe surface of chip 31. The chip 31 and its circuitry elements may becompletely encapsulated within a molded body 32 of electricallyinsulative material, such as a suitable resinous plastic material,defining an insulative wall 33 at the underside of the circuitryelements engageable with the outer surface of the suitcase, and defininga wall 34 at the upper or outer side of the chip 31 and its carriedcircuit. This encapsulating insulative body 32 may have flangesextending about its periphery at 35, secured to the suitcase byfasteners 36 or otherwise. It is also contemplated that the device maybe secured to the suitcase by adhesive, or in any other convenientmanner.

Above wall 36 formed by the insulative encapsulating material, thismaterial forms and defines an elongated slot 37, which is opened only atits left end 38, and into which the previously mentioned key 19 isslidably receivable in the closely confined and accurately locatedrelation illustrated in FIG. 3. This key is normally in the possessionof the owner of the suitcase, and is inserted into slot 37 at the timethat the owner receives his bag from support platform 16 of FIG. I, tothereby place the device 18 in a condition for indicating to the radioequipment 17 at the exit opening 13 that the person carrying the bag isauthorized to remove it from the area.

In the particular arrangement illustrated in FIG. 3, the key 19 isassumed to be formed of an electrically insulative material, such as asuitable rigid resinous plastic material, except at the location of twoelectrically conductive metal inserts 39 and 40. These inserts areengageable with contacts 41, 42, 43 and 44 projecting upwardly from thecircuitry formed on integrated circuit chip 31, so that when the key isin the FIG. 3 position, metal element 39 will engage and form a shortcircuit between contacts 411 and 42, while element 40 will engage andform a short circuit between contacts 43 and 44. From the schematicrepresentation of FIG. 4, it will be apparent that the contacts thenform short circuits across both of the antenna coils 27 and 29, andthereby disable circuit 26 against functioning as a transponder in thepreviously discussed manner. The circuit 26 will then not serve totransmit any radio signal in response to reception of the signal fromfixed transmitter 20.

To now recapitulate the manner of use of the device illustrated in FIGS.1 to 45, assume that transmitter 20 is functioning continuously to emita radio signal of a predetermined radio frequency, and that receiver 22will respond only to the second harmonic of that frequency. Also assumethat the various bags 15 being delivered onto platform 16 from conveyor14 are provided with transponder devices of the type illustrated at 18,but that these devices are ineffective to transmit any substantialdetectable signal to receiver 22 when the bags are in the right-handportion of the room 11 of FIG. I. The transmitter 20 may if desired bemade directional, to aim its transmission primarily across the exitdoorway in the direction indicated at 45 in FIG. I, while the antenna ofreceiver 22 may be made similarly directional to receive radio signalsbest and primarily in the direction indicated at 46 in FIG. 1. Also, theintensity of the transmitted signal, the sensitivity of receiver 22, andthe components of circuit 26 of the transponder devices 18 may all be soselected and designed as to enable the receiver 22 and indicator 23 torespond only to the devices 18 individually, as each separate bag iscarried out of the exit opening 13.

If an unauthorized person picks up one of the bags 15 from the locationas and attempts to carry it from the room through exit opening 13, thesignal emitted by transmitter 20 will be received by antenna 27 of thedevice 18 on that particular bag, will be rectified by the full waverectifier 28, and will cause transmission of a response signal ofdoubled frequency from antenna 29 to receiver 22. The receiver in turnwill energize indicator 23 to emit an audible or visual signal, or thelike, indicating to an attendant that an unauthorized removal of the baghas been attempted. If the person is the true owner of the bag, on theother hand, he merely inserts key 19 into slot 37 of FIG 3, to form ashort circuit across both of the coils 27 and 29 in a manner disablingthe circuit, As previously described, so that device 18 cannot transmitthe harmonic frequency signal, and indicator 23 is not actuated. Thereceiver 22 is of course tuned accurately to the harmonic frequency, andincludes filter circuits which filter out the fundamental frequency oftransmission of the transmitter 20, and all other unwanted frequencies,so that there is no response of the receiver and indicator unless theprecisely predetermined harmonic frequency is received. Also,transmitter 20 must be filtered effectively to produce a purefundamental frequency, without harmonics, so that the signal from thetransmitter cannot in any way serve to directly actuate the receiver,without the interaction of frequency doubling transponder device 18.

Instead of disabling the circuitry, the key 19 or its equivalent mayupon insertion serve to convert the circuit from a disabled condition toan active condition, to transmit a signal for reception by receiver 22only when the key is inserted, and thereby indicate authorization raterthan nonauthorization of the person. Also, as previously indicated, thesignals received by receiver 22 may control the operation of theturnstile, to either allow a person to leave the area, or prevent hisleaving, in accordance with the reception ofa control signal by receiver22 from device I8.

FIG. 6 shows a variational device which may be utilized for indicatingan attempt to remove from a store or other area an article 150, whichmay typically be an article of merchandise displayed for sale in thestore. The device of FIG. 6 may be very similar to transponder device 18of FIGS. I to 4, except for the deletion of key 19 and the contacts tobe engaged thereby. The integrated circuit 26a of FIG. 6 may beotherwise identical with circuit 26 of FIG. 4, and may be formed on asilicon chip such as that illustrated at 31 in FIG. 3, and be completelyencapsulated within an electrically insulative material 32a. Theencapsulated unit is adapted to be attached in any suitable manner tothe article of merchandise a or other article, as by provision of alayer of pressure sensitive adhesive 47 on one surface of the capsule,and/or by provision of a flange or tab 48 on the capsule, typicallycontaining an opening 49 by which the capsule may be pinned or otherwisefastened to an article of clothing or other piece of merchandise to beprotected.

When an unauthorized person attempts to remove the article 15a from theselling area or room, he must in leaving the room pass a transmittersuch as that shown at in FIG. 1, a receiver 22, indicator 23, etc. Uponreception of the signal emitted by transmitter 20 the device 18a of FIG.6 will transmit a response signal of doubled or other harmonic frequencyserving to actuate the indicator 23 or other unit serving as an alarmfor apprising an attendant of the attempted theft. When an articlecarrying one of the devices 18a is sold, a sales person may remove thetransponder device 18a, or alternatively may merely bring the devicenear a highly powered transmitter represented diagrammatically at 50 inFIG. 6, in a manner such that the radio signal emitted by transmitter 50will produce in the coils 27a and 29a of the integrated circuit indevice 180 a current so great as to purposely burn out or destroy one ormore of the diodes 30 or other components of the integrated circuit, andthereby disable it in a manner such that it will not subsequentlyactuate the alarm system when the purchaser passes the transmittingequipment upon leaving the sales area.

The device 18a of FIG. 6, or other variations of the invention, may alsobe used on or as identification badges, to be worn or carried by personsin a manufacturing plant or the like, for indicating whether thesepersons are authorized to enter or leave a particular area policed by atransmitter, receiver, etc., as shown in FIG. I. In that case, theidentification badge or the device 18a itself becomes the article whosemovement between areas is either authorized or unauthorized, and is tobe controlled by the monitoring equipment.

While certain specific embodiments of the present invention have beendisclosed as typical, the invention is of course not limited to theseparticular forms, but rather is applicable broadly to all suchvariations as fall within the scope of the appended claims.

I. Apparatus for detecting an attempted unauthorized movement of anarticle between two areas, comprising means for transmitting a firstradio signal at or near said areas, circuitry carried by said articleresponsive to said first signal and operable to transmit a second anddifferent radio signal, means responsive to said second signal andoperable to indicate whether an attempted movement of said article isauthorized, and a control key device which is separable from saidarticle and is adapted to alter the response of said circuitry to saidfirst signal in a manner which may be sensed by said last mentionedmeans to indicate that a person having the key device is authorized tomove the article.

2. Apparatus as recited in claim 1, in which said circuitry in apredetennined normal condition is responsive to said first signal toproduce said second signal, said control key device being operable todisable the circuitry against transmission of said second signal.

3. Apparatus as recited in claim 1, in which said circuitry includes anantenna for receiving said first signal, a rectifier for producing saidsecond signal from said first signal at a frequency which is a harmonicof the frequency of the first signal, and an antenna for emitting saidsecond signal, said key device being movable to a predetermined positionrelative to said circuitry and operable to short circuit said circuitryin a relation preventing transmission of said second signal, there beingmeans on said article defining a receptacle for removably retainingsaidkey at said position.

4. Apparatus as recited in claim 1, in which said circuitry includes anantenna for receiving said first-signal, a rectifier for rectifying thereceived first signal to produce an output of doubled frequency, and atransmitting antenna for transmitting said second signal at said doubledfrequency.

5. Apparatus as recited in claim 1, including holder means for removablyreceiving and holding said key device at a predetermined active positionin which its presence has an effect on said second signal.

6. A device for detecting an attempted unauthorized movement of anarticle between two areas, comprising a structure to be carried by thearticle and having circuitry adapted to receive a first radio signalfrom a transmitter at or near said areas, and responsive to said firstsignal to produce a second and different radio signal for indicating bysaid secondsignal whether an attempted movement of the article isauthorized, and a control key device which is separable from saidstructure and adapted to be carried by an authorized person and isadapted to alter the response of said circuitry to said first signal ina relation indicating that the person is authorized.

7. A device as recited in claim 6, in which said circuitry is atransponder circuit utilizing the received power of said first signal toproduce said second signal.

8. A device as recited in claim 6, including holder means for removablyreceiving and holding said key device at a predetermined active positionin which its presence has an efiect on said second signal.

9. A device as recited in claim 6, in which said circuitry includesantenna means for receiving said first signal, rectifier means forrectifying said first signal and producing said second signal at afrequency which is a harmonic of the frequency of the first signal, andantenna means for emitting said second signal, there being a socket forremovably receiving said key device, said key device being operable whenin said socket to disable said circuitry against production of saidsecond signal.

10. The combination comprising an article which may be removed from apredetermined area, and a device carried by said article for indicatingan attempted unauthorized removal of the article from said area, saiddevice including circuitry adapted to receive a first radio signal froma transmitter at or near said area, and responsive to said first signalto produce a second and different radio signal for indicating by saidsecond signal whether an attempted removal of the article is authorized,and a control key which is separable from said device and is adapted toalter the response of said circuitry to said first signal in a relationindicating that a person having said key is authorized.

11. The combination as recited in claim 10, in which said article is anarticle of baggage.

12. The method of detecting an attempted unauthorized movement of anarticle between two areas,comprising requiring said article to becarried past a detection station if it is moved between said areas,transmitting a radio signal to said article as it passes said station,providing the article with circuitry responsive to said transmittedsignal and operable to transmit a second radio signal, monitoring saidsecond signal as an indication of whether an unauthorized movement ofthe article is being attempted, applying a key to said circuitry ifmovement of said article is authorized, changing the condition. of saidcircuitry by use of said key, and detecting said change in condition ofthe circuitry through a change in said second signal.

13. Apparatus for detecting an attempted unauthorized movement of anarticle between two areas, comprising circuitry carried by said articleand operable to transmit a radio signal which is to be monitored by areceiver and which indicates whether said movement of the article isauthorized, and a key which is separable from said article and isadapted to alter the transmission of said radio signal in a manner whichmay be sensed by said receiver to indicate that a person having the keyis authorized.

14. The method of detecting attempted unauthorized movement of any of anumber of articles between two ares, comprising requiring said articlesto be carried past a detection station upon such movement, monitoringradio signals received from circuitry carried by said articles as theyare moved past said station, converting said circuitry of any articleauthorized for said movement to a condition different from that of anyarticles not authorized for said movement by means of keys carried byauthorized persons and separable from said articles, and distinguishingbetween said authorized and unauthorized articles by differences in saidmonitored radio signals.

15. Apparatus for controlling movement of an article between two areas;comprising means to be located at or near said areas and operable totransmit a first radio signal to circuitry carried by said article;means for receiving a response signal from said circuitry anddetermining therefrom whether or not said movement of the article isauthorized; a turnstile or other movement controlling structure betweensaid areas; and

means controlling operation of said turnstile or other movementcontrolling structure in correspondence with changes in said responsesignal.

16. The method of detecting an attempted unauthorized movement of anarticle between two areas, comprising requiring said article to becarried past a detection station if it is moved between said areas,transmitting a radio signal to said articles as it passes said station,providing the article with circuitry responsive to said transmittedsignal and operable to transmit a second radio signal, monitoring saidsecond signal as an indication of whether an unauthorized movement ofthe article is being attempted, and applying to said circuitry a thirdradio signal intense enough to purposely destroy its capacity to producesaid second signal, if said movement of the article is to be authorized.

1. Apparatus for detecting an attempted unauthorized movement of anarticle between two areas, comprising means for transmitting a firstradio signal at or near said areas, circuitry carried by said articleresponsive to said first signal and operable to transmit a second anddifferent radio signal, means responsive to said second signal andoperable to indicate whether an attempted movement of said article isauthorized, and a control key device which is separable from saidarticle and is adapted to alter the response of said circuitry to saidfirst signal in a manner which may be sensed by said last mentionedmeans to indicate that a person having the key device is authorized tomove the article.
 2. Apparatus as recited in claim 1, in which saidcircuitry in a predetermined normal condition is responsive to saidfirst signal to produce said second signal, said control key devicebeing operable to disable the circuitry against transmission of saidsecond signal.
 3. Apparatus as recited in claim 1, in which saidcircuitry includes an antenna for receiving said first signal, arectifier for producing said second signal from said first signal at afrequency which is a harmonic of the frequency of the first signal, andan antenna for emitting said second signal, said key device beingmovable to a predetermined position relative to said circuitry andoperable to short circuit said circuitry in a relation preventingtransmission of said second signal, there being means on said articledefining a receptacle for removably retaining said key at said position.4. Apparatus as recited in claim 1, in which said circuitry includes anantenna for receiving said first signal, a rectifier for rectifying thereceived first signal to produce an output of doubled frequency, and atransmitting antenna for transmitting said second signal at said doubledfrequency.
 5. Apparatus as recited in claim 1, including holder meansfor removably receiving and holding said key device at a predeterminedactive position in which its presence has an effect on said secondsignal.
 6. A device for detecting an attempted unauthorized movement ofan article between two areas, comprising a structure to be carried bythe article and having circuitry adapted to receive a first radio signalfrom a transmitter at or near said areas, and responsive to said firstsignal to produce a second and different radio signal for indicating bysaid second signal whether an attempted movement of the article isauthorized, and a control key device which is separable from saidstructure and adapted to be carried by an authorized person and isadapted to alter the response of said circuitry to said first signal ina relation indicating that the person is authorized.
 7. A device asrecited in claim 6, in which said circuitry is a transponder circuitutilizing the received power of said first signal to produce said secondsignal.
 8. A device as recited in claim 6, including holder means forremovably receiving and holding saId key device at a predeterminedactive position in which its presence has an effect on said secondsignal.
 9. A device as recited in claim 6, in which said circuitryincludes antenna means for receiving said first signal, rectifier meansfor rectifying said first signal and producing said second signal at afrequency which is a harmonic of the frequency of the first signal, andantenna means for emitting said second signal, there being a socket forremovably receiving said key device, said key device being operable whenin said socket to disable said circuitry against production of saidsecond signal.
 10. The combination comprising an article which may beremoved from a predetermined area, and a device carried by said articlefor indicating an attempted unauthorized removal of the article fromsaid area, said device including circuitry adapted to receive a firstradio signal from a transmitter at or near said area, and responsive tosaid first signal to produce a second and different radio signal forindicating by said second signal whether an attempted removal of thearticle is authorized, and a control key which is separable from saiddevice and is adapted to alter the response of said circuitry to saidfirst signal in a relation indicating that a person having said key isauthorized.
 11. The combination as recited in claim 10, in which saidarticle is an article of baggage.
 12. The method of detecting anattempted unauthorized movement of an article between two areas,comprising requiring said article to be carried past a detection stationif it is moved between said areas, transmitting a radio signal to saidarticle as it passes said station, providing the article with circuitryresponsive to said transmitted signal and operable to transmit a secondradio signal, monitoring said second signal as an indication of whetheran unauthorized movement of the article is being attempted, applying akey to said circuitry if movement of said article is authorized,changing the condition of said circuitry by use of said key, anddetecting said change in condition of the circuitry through a change insaid second signal.
 13. Apparatus for detecting an attemptedunauthorized movement of an article between two areas, comprisingcircuitry carried by said article and operable to transmit a radiosignal which is to be monitored by a receiver and which indicateswhether said movement of the article is authorized, and a key which isseparable from said article and is adapted to alter the transmission ofsaid radio signal in a manner which may be sensed by said receiver toindicate that a person having the key is authorized.
 14. The method ofdetecting attempted unauthorized movement of any of a number of articlesbetween two ares, comprising requiring said articles to be carried pasta detection station upon such movement, monitoring radio signalsreceived from circuitry carried by said articles as they are moved pastsaid station, converting said circuitry of any article authorized forsaid movement to a condition different from that of any articles notauthorized for said movement by means of keys carried by authorizedpersons and separable from said articles, and distinguishing betweensaid authorized and unauthorized articles by differences in saidmonitored radio signals.
 15. Apparatus for controlling movement of anarticle between two areas; comprising means to be located at or nearsaid areas and operable to transmit a first radio signal to circuitrycarried by said article; means for receiving a response signal from saidcircuitry and determining therefrom whether or not said movement of thearticle is authorized; a turnstile or other movement controllingstructure between said areas; and means controlling operation of saidturnstile or other movement controlling structure in correspondence withchanges in said response signal.
 16. The method of detecting anattempted unauthorized movement of an article between two areas,comprising requiring said article to be carrIed past a detection stationif it is moved between said areas, transmitting a radio signal to saidarticles as it passes said station, providing the article with circuitryresponsive to said transmitted signal and operable to transmit a secondradio signal, monitoring said second signal as an indication of whetheran unauthorized movement of the article is being attempted, and applyingto said circuitry a third radio signal intense enough to purposelydestroy its capacity to produce said second signal, if said movement ofthe article is to be authorized.